Multimodal Deformation Mechanism of the Swelling-Induced Hydrogel Actuators

Hydrogels, known for their adjustable mechanical properties and exceptional responsiveness to environmental stimuli, provide an important material foundation for soft adaptive structures. However, current research on hydrogel-based actuators and negative swelling metamaterials primarily focuses on gradient structural designs, which limit the range and diversity of deformations. This study introduces an innovative design strategy for hydrogel-based actuator unit cells, inspired by the natural opening and closing motions observed in biological structures. We developed a composite deformation unit cell consisting of hydrogel blocks and a polymeric rhombic frame, where the hydrogel's swelling induces bending in the frame, leading to unit cell deformation. Through analytical modeling and finite element simulations, this research systematically explores how geometric parameters affect the linear strain of the unit cells. Based on these findings, tunable anisotropic swelling deformations can be achieved in both two-dimensional and three-dimensional forms. Additionally, we have developed hydrogel-based actuators capable of multimodal deformations, including bending, twisting, and complex shape transformations. This work introduces a novel design concept for hydrogel-based actuators, offering new insights into the design of adaptive structural materials for future unmanned aerial systems.